Next Generation Wireless Local Area Networks (WLANs), 802.11n and 802.11 ac, are expected to provide efficient, ubiquitous, and high-speed Internet access for multimedia applications such as HDTV (20 Mbps) and DVD (9.8 Mbps). To ensure user satisfaction, the Quality of Service (QoS) provided by WLANs should be comparable to that of wired networks. As a result, several recent 802.11n/ac amendments have proposed frame aggregation and Block Acknowledgement (BA) techniques for improving the transmission efficiency by reducing the MAC/PHY overhead.
However, the inherent error-prone nature of wireless communications results in a high packet error rate and the corrupted aggregated frame causes significant retransmission overhead. Consequently, an urgent requirement exists for efficient retransmission schemes to enhance the performance of high-speed WLANs.
Referring the FIG. 1 is a flowchart of stop and wait scheme when error happened in the traditional 802.11n/ac. If one of the MPDUs within A-MPDU has not been positively acknowledged or reach the retry limitation, the whole frame should be retransmitted.
Hybrid Automatic Repeat reQuest (HARQ) error-control methods have been widely used to mitigate packet losses in wireless systems. Although the Hybrid Automatic Repeat reQuest (HARQ) error-control method recovers from packet loss, it has low transmission efficiency and is unsuitable for frame aggregation transmission of 802.11n/ac. However, most HARQ schemes do not account for frame aggregation effects.
In an attempt to address this problem, the inventor has presented several Aggregated Selective Repeat (ASR) ARQ schemes in “Novel Design and Analysis of Aggregated ARQ Protocols for IEEE 802.11n Networks” IEEE Trans. on Mobile Computing. FIG. 2 shows the flow diagram of MPDUs de-aggregation procedure for ASR-ARQ scheme. Using compressed Block ACK (BA) for acknowledging the entire A-MPDU; checking if each MPDU with A-MPDU is correct via frame check sequence (FCS); and retransmitting unsuccessfully transmitted MPDUs until all the MPDUs within A-MPDU have either been positively acknowledged or reached the retry limitation. However, the retransmitted packets do not fully utilize the potential benefits of frame aggregation since they only be retransmitted alone without aggregating with new packets. That is, the protocols follow the conventional ASR scheme in only sending the retransmitted packets in the next frame.
ASR-ARQ does not make efficient use of the available bandwidth since only the packet(s) corresponding to corrupted packet(s) are retransmitted in the following A-MPDU. As a result, the potential benefits of frame aggregation are significantly reduced.
Network Coding (NC) has emerged as one of the most promising information theoretic techniques for improving the performance of computing networks. Several recent studies have applied Random Linear Coding (RLC) techniques to mitigate the HARQ unicast retransmission overhead in wireless broadband networks. In general, RLC has shown significant benefits in wired/wireless networks and is expected to yield similar benefits in 802.11n/ac networks with frame aggregation features.
In order to solve the problem(s), the present invention introduces a method for frame aggregation transmission of wireless network system with network coding to improve transmission efficiency.